In the last 24 hours, all the major rivers were flowing above the danger level, leading to embankment breaches.
There were reports of fresh floods in three new districts of Saharsa, Katihar and Purnea.
Dozens of villages have been inundated that have forced people to flee their homes and seek shelter at safer places, a disaster management official said.
In the worst hit Sitamarhi and Araria districts, roads have also been damaged.
The floods were caused by heavy rain in north Bihar and the catchment areas of major rivers in neighbouring Nepal.
However, Water Resources Department officials said the water level in rivers originating in Nepal was likely to decrease as rain in those areas have stopped.
Chief Minister Nitish Kumar carried out an aerial survey of the affected Seemanchal and Koshi region on Sunday and Monday. He will inform the Bihar Assembly on Tuesday about the situation.
To date, 196 relief camps have been set up in the affected areas, with 644 community kitchens providing food to the displaced people.
The Disaster Management Department said relief and rescue operations were continuing in the flood-affected areas.
A total of 26 companies of the National Disaster Response Force, State Disaster Response Force and Seema Sashatra Bal have been deployed to carry out the operations.
( With inputs from IANS )